The New York Times reported last month that Corallo planned to testify that Hicks told President Trump in a phone call that news of a 2016 meeting between Trump campaign staffers and a Russian lawyer in Trump Tower “will never get out.” The comment sparked concerns that Hicks might be considering obstructing justice.

The former spokesman also hired a pair of D.C. lawyers in anticipation of interviewing in the probe.

“Mark Corallo was instructed not to speak to the press, indeed not to even answer the phone,” Wolff wrote. “Later that week, Corallo, seeing no good outcome — and privately confiding that he believed the meeting on Air Force One represented a likely obstruction of justice — quit.”

Mueller is reportedly focusing on the Trump Tower meeting in his probe.

The special counsel is also seeking an interview with Trump, which the president has said he would be open to. However, Trump said the final decision on an interview would be made by his attorneys, and his lawyers are reportedly warning against it.